X-MEN star Jackman opens his heart on the painful effort to fit the role of Jean Valjean in the blockbuster movie aswell as his father's battle with Alzheimer's.

THANKS to his role as hulking X-Men superhero Wolverine, Hugh Jackman is one of Hollywood’s most recognisable stars.

But even his ardent fans may have a little trouble identifying him in the opening scenes of the big budget film version of musical Les Miserables.

Haggard, shaven-headed and sporting a scraggly grey beard, he looks a shadow of his former self.

And Hugh admits his portrayal of convict-turned-hero Jean Valjean is the most gruelling part he has ever played.

He says: “The director told me ‘I need you to get to where your friends stop you and ask, ‘Are you OK? Are you sick?’. Until you get to that point you haven’t gone far enough’.

“It took me to places I’ve never been before, vocally, physically, emotionally.

“I told my wife, ‘This may be too much for me’. She replied, ‘It will probably demand more of you than anything you’ve done so it should feel frightening and uncomfortable’. She told me, ‘Use the fear. Work harder. Get in there’.

“I shaved my head, had to lose more than two stone in weight and lived like a monk, nursing my vocal cords with a portable steam machine and avoiding dairy products.

“I went off coffee because it doesn’t help the voice and if I didn’t have eight hours’ sleep a night, forget it. Some days I started singing at nine in the morning and was still singing at 10 at night so it wasn’t easy.”

Ian West/PA

Hugh with co-stars Russell Crowe and Anne Hathaway

The genial 44-year-old Australian is being tipped for Oscars glory for his gut-wrenching performance in the film.

But he faces an even more devastating challenge in his personal life as his beloved dad Chris, who raised him alone, sinks deeper into the grip of Alzheimer’s disease.

Hugh says: “He still recognises me and can talk about the past. Weirdly, he’s as happy as I’ve ever known him, which is wonderful.”

Hugh’s English parents emigrated to Oz a year before he was born, and split when he was eight. His mum returned to England and raised the couple’s two daughters.

Chris stayed in Oz with their three boys. “The greatest gift I got from him was his unconditional love,” says Hugh.

“He always talked about passion. He never asked what I was going to do. He only ever said, ‘Do you love what you’re doing?’ If there’s anything I want to pass on to my kids it’s the idea of passion for life, because that’s what sustains you.”

Hugh was recently in his home city of Sydney filming The Wolverine and was able to spend a lot of time with his dad.

But for now he is promoting Les Mis and says he loved director Tom Hooper’s decision to have the actors singing as cameras rolled, rather than lip-syncing as is usual in musicals.

“As a performer it was fantastic,” says Hugh. “The idea of singing live was daunting at first but it gave me so much freedom. It was like being on stage.

“Instead of lip-syncing I could slow the tempo down or speed it up and do what I liked. I just had to worry about acting.”

Before filming began he and the other leading cast members – Russell Crowe, Anne Hathaway, Amanda Seyfried and Eddie Redmayne – spent a solid two months rehearsing.

“You can’t just turn up to a musical and hope to do it,” Hugh says. “This wasn’t sitting around chatting. This was serious so by the time we started filming we had a great ensemble feeling and we were all in it.”

Another united team is the Jackman family.

Hugh and wife Deborra-Lee Furness, 57, have two adopted children, Oscar, 12, and seven-year-old Ava. And they all travel together wherever Hugh’s work takes them.

Evan Agostini/Invision/AP

Showing off his wife Deborra-Lee

They had a house in Pimlico in central London for three years but now they spend most of their time in New York. “It wasn’t planned, but we’ve been gypsies since 1998,” he says.

“We always travel together and have a rule of not being apart for more than two weeks. I cherish the everyday moments like cooking pancakes on Sundays.

“At home I’m the steady, sensible one and Deb is the fun, sexy, crazy one.”

The couple got hitched 16 years ago after meeting while they starred in Australian prison drama Corelli.

Hugh says: “I had a mullet haircut, tattoos and I was jacked up from the gym. That’s how she fell in love with me. She kind of likes the bad boys.”

His role as the mutant with razor-sharp claws made him an international star in 2000 after a string of roles on stage and the small screen.

Despite hosting the Oscars in 2009 and being named in a poll as the world’s sexiest man, he remains a down-to-earth Aussie who enjoys a beer and appreciates his luck.

He says the biggest bonus about Les Mis wasn’t the money but working for the first time with old Aussie pal Russell Crowe, who plays Javert, the policeman who pursues Jean Valjean.

“It was an absolute joy working with him,” says Hugh.

“Parties at Russell’s place always involve singing. One of the first days on the movie he called up at 9pm and goes, ‘Come on, mate. Do you want to have a bit of a sing?’ So we went to his place and started singing and just went on.”

There’s something else that Hugh is singing from the rooftops – the debt of gratitude he owes his dad.

Hugh says: “I see a lot of Jean Valjean in my dad.

“My dad is a hard worker, very humble and deeply religious. Everything about him is admirable.

“He’s never said a bad word about anybody.

“He’s been my rock and if there are any good qualities about me it’s largely due to my dad.”